In recent years, study has been forwarded to control the airflow rates independently for the driver's seat and the assistant's seat to meet the requirements of the users of the vehicles. The above requirements have been heretofore been satisfied by controlling the airflow rate through the refrigerant evaporator independently on the right side and on the left side in the direction of core width. When the airflow rate is to be independently controlled on the right side and on the left side of the refrigerant evaporator in which the heat-exchanging tubes are longitudinally arranged, it has been necessary for the refrigerant evaporator to have a structure in which a separator is inserted in a tank to separate the flow of refrigerant in the direction of core width, so that the refrigerant flows through passages that are different depending on the right side and the left side.
This, however, results in an increase in the distance of the refrigerant flow passages and, hence, in an increase in the pressure loss making it difficult to improve performance of the refrigerant evaporator. To cope with this, therefore, the present inventors have proposed a refrigerant evaporator as disclosed in Japanese Patent Application No. 2003-434216 (U.S. patent application Ser. No. 10/827,559). According to this refrigerant evaporator, the refrigerant flowing through a first path on the front surface is folded to a second path on the back surface and, at this moment, the flow is changed over right side left to decrease the pressure loss on the refrigerant side, to improve the temperature distribution and to independently control the airflow rate on the right side and on the left side (hereinafter, this new refrigerant path system is referred to as front-and-rear right-and-left cross path).
The problem, however, has been how to realize the heat exchanger having the front-and-rear right-and-left cross path in a simple constitution that facilitates the mass production.